I did search for this answer ahead of time, this popped up in a recent game.

At the end of a play round, are you required to have all your race tokens on the board or can you hold them off the map until next round?

At the end of your turn, if you still have tokens in your hand (because you failed a reinforcement roll or something) you place the tokens in regions that you already control. There is no reason why you would want to keep tokens in your hand...and if we use the iPad app as a reference, you must place all your tokens on the board unless you are Barbarians (available in one of the expansions).

{quote]What if you do not have a region for them? Meaning your last region was attacked and conquered, one of your race tokens was returned to the tray, and you now have 1 race token in holding?

Thanks[/quote]

If you have been kicked off the board because of attacks, and you no longer have any regions, you keep the tokens in your hand. Then if you decide to go into Decline (like in your example, you have 1 token left) then you will take all of your older In Decline tokens off the board and will score no points for the turn.